This invention relates to an apparatus that estimates the amount of air coming into a cylinder.
One well-known apparatus is a mechanism in which an amount of air coming into an internal combustion engine (air-flow amount Q) is detected by an air-flow meter, and then, fuel injection amount and spark timing are controlled based on the detected air-flow amount Q and an engine speed .omega.. This type of apparatus is constructed so that an intake air amount mc coming into the cylinder during an intake stroke can be described by the following equation (1) based on the air-flow amount Q detected by the air-flow meter and on the engine speed .omega.. EQU mc=K.multidot.Q/.omega. (1)
where K is a constant.
The control amount of the engine is determined based on the air-flow amount Q and the engine speed so the desired air/fuel ratio of air-fuel mixture coming into the cylinder can be controlled or spark timing can be controlled to obtain an optimum output torque.
The engine controlled as above is well-controlled during the steady operation, but in transitional operation with a change in driving conditions, the air/fuel ratio or spark timing can not be controlled well according to the operation states of the engine. This is because the air-flow amount Q detected by the air-flow meter does not correspond to the actual intake air amount mc coming into the cylinder due to a surge tank in the intake pipe for suppressing the surges of intake air.
Specifically, when the engine starts decelerating, air that has passed through the air-flow meter is temporarily stored in the surge tank so that the intake air amount coming into the cylinder is less than that estimated by Q/.omega.. On the other hand, when the engine starts accelerating, air in the surge tank enters the cylinder so that more air than the amount detected by the air-flow meter enters the cylinder. For this reason, accuracy in fuel injection control and spark timing control deteriorates during transitional operation of the engine.